1. Field of the Invention
This invention relates to a noise filter for connectors and paticularly to a noise filter using capacitors.
2. Description of the Prior Art
FIG. 1 is a longitudinal section showing part of a connector having a conventional noise filter incorporated therein. The connector 1 has a grounded metal case 2. Installed in the case 2 is a base plate 3 of an insulating nature, from which a plurality of pins 4 project. The pins 4 are received by a mating connector (not shown) which is to be connected to the connector 1 and thereby establishes an electric connection.
Usually, in such connection, noise is produced. To eliminate such noise, a noise filter is built in the connector 1. For example, the noise filter is constituted of a cylindrical capacitor 5. The cylindrical capacitor 5 is in the form of a hollow cylindrical body having a throughgoing hole through which the pin 4 extends. The inner peripheral surface defining the throughgoing hole has an inner electrode formed thereon, which electrode will be electrically connected to the pin 4. The outer peripheral surface of the cylindrical capacitor 5 has an outer electrode formed thereon, which electrode will be electrically connected to the metal case 2. Insulating resin 6 is formed to cover the cylindrical capacitors 5 except the front end portions of the pins 4.
With the connector 1 thus arranged, noise from the outside is eliminated by the cylindrical capacitors 5. If, however, a noise filter of this type is employed additional steps are, there is a required to establish an electric connection between each pin 4 and each cylindrical capacitor 5: As a result, the prior art connector exhibits the drawback of requiring significant time and labor in producing such connectors 1.
FIG. 2 is a perspective view showing the external appearance of another conventional noise filter used in a connector. FIG. 3 shows the lower surface of the noise filter shown in FIG. 2. An insulating base plate 8 through which a plurality of pins 7 extend is formed of a dielectric material. One surface of the insulating base plate 8 is formed with electrodes 9, e.g., four in number, separated from each other, while the other surface is formed with a single electrode 10 throughout. The first electrodes 9 will later be electrically connected respectively to the pins 7. There is an insulating gap 11 formed between the other electrode 10 and each pin 7. When this noise filter is built in a connector, the electrode 10 is grounded.
The noise filter shown in FIGS. 2 and 3 encounters a problem of stray capacity. For example, such stray capacity presents itself between divisional electrodes 9, causing interference and making satisfactory elimination of noise impossible. Further, the formation pattern of the electrodes 9 must be selected in accordance with the disposition of the pins 7 used in the connector, thus limiting flexibility in designing such noise filters, and making the production difficult.